UL is the abbreviation of Underwriter Laboratories Inc. in the United States. The UL Safety Testing Laboratory is the most authoritative in the United States and is also a relatively large private institution in the world engaged in safety testing and certification. It is an independent, non-profit professional institution that conducts tests for public safety. It uses scientific testing methods to study and determine whether various materials, devices, products, equipment, buildings, etc. pose hazards to life and property and the extent of such hazards; it determines, compiles, and issues corresponding standards and materials that help reduce and prevent losses to life and property, and at the same time conducts fact-finding research services.

Introduction to UL
UL is mainly engaged in product safety certification and safety certification operation services. Its ultimate goal is to ensure that the market has products with a considerable safety level and to contribute to the guarantee of personal health and property safety. In terms of product safety certification as an effective means to eliminate technical barriers to international trade, UL also plays an active role in promoting the development of international trade.
UL was founded in 1894. In the initial stage, UL mainly relied on funds provided by the fire insurance department to maintain its operation. It was not until 1916 that UL became completely self-sufficient. After nearly a century of development, UL has become a certification institution with world-renowned reputation, and it has a set of strict organizational management systems, standard development, and product certification procedures. UL is managed by a council composed of representatives from safety experts, government officials, consumers, the education sector, public utilities, the insurance industry, and standards departments. The daily work is handled by the president and vice presidents. Currently, UL has five laboratories in the United States. Its headquarters is located in the town of Northbrook, north of Chicago. At the same time, corresponding laboratories have been established in Taiwan and Hong Kong respectively. In the United States, for consumers, UL is a symbol of the safety mark. Globally, UL is one of the most trusted providers of conformity assessment for manufacturers.

Introduction to the UL Mark
Style of the UL Mark
The UL mark is usually labeled on the product and/or product packaging to indicate that the product has passed the UL certification and meets the safety standard requirements.
Composition
The most important part of these marks is the UL logo symbol, and these symbols are all registered trademarks of UL.
Requirements for the Use of the UL Mark

1. The minimum height of the registered trademark should be 3/64 inches.

2. When the outer diameter of the UL mark is less than 3/8 inches, the registered trademark symbol can be ignored if it is not clearly readable to the naked eye.

3. The mark can be directly and permanently affixed to the unchanging product by stamping, molding, ink printing, screen printing, or similar methods.

4. Acquisition of the mark: Manufacturers can reprint it or obtain it from UL-authorized distributors.

5. The ULus mark (only "us", no "c"): A safety mark for products entering the US market; cUL (only "c", no "us"): A safety mark for products entering the Canadian market; the cULus mark: A safety mark for products entering both the US and Canadian markets.

Service Items
The types of UL product certification and testing services can mainly be divided into Listing, Recognition, and Classification.

1. Listing:
Generally speaking, listing is only applicable to complete products and various devices and installations that can be replaced or installed on-site by qualified personnel. Various products under UL listing services include: household appliances, medical equipment, computers, commercial equipment, and various electrical products used in buildings, such as power distribution systems, fuses, wires, switches, and other electrical components. Products listed by UL can usually be marked with the UL listing mark on each product. Usage of the listing mark.

2. Recognition:
The recognition service is one of the items in UL services. The products identified can only be used as components and raw materials on UL-listed, classified, or other recognized products. Recognized products are not complete in structure or have certain restrictions in use to ensure the expected safety performance. In most cases, the follow-up service for recognized products belongs to category R. Recognized products belonging to category L include electronic wires (AVLV2), processed wires (ZKLU2), wire harnesses (ZPFW2), aluminum wires (DVVR2), and flexible metal conduits (DXUZ2). Recognized products are required to carry the recognition mark.

3. Classification:
The classification service only evaluates the specific hazards of products or evaluates products that comply with other standards (including internationally recognized standards such as IEC and ISO standards) other than UL standards. Generally speaking, most classified products are not products used by consumers but products used in industry or commerce. The classification mark in the UL mark indicates that there are certain restrictive conditions and specified scopes when the product is identified by UL. For example, for chemical products such as industrial solvents, only the range of possible fires when the flash point temperature is reached is evaluated. The classification service for some products is the same as the listing service, but generally, only one or several aspects of the product are evaluated. For example, in the United States, medical X-ray diagnostic equipment and other such devices must comply with US laws and relevant regulations on radiation emission and beam accuracy across the country. However, since UL only classifies X-rays as classified products, only their mechanical performance, electrical performance, and other non-radiation performances are evaluated.

4. Multiple Listing, Multiple Recognition, or Multiple Classification Services:
When a UL applicant, after obtaining the above-mentioned listing, recognition, or classification service, wants to produce the product in the name of another company to meet the sales needs, he can apply for multiple listing, multiple recognition, or multiple classification services. In this case, the manufacturer that has obtained the listing, recognition, or classification is allowed to use the name of another company in the product catalog, but the product, except for the company code, product code, or other features that UL deems acceptable, must be consistent with the original listed, recognized, or classified product.

5. "AL" Listing, Recognition, or Classification Service
If a UL applicant does not want to obtain the listing, recognition, or classification service in the name of his own company, he can apply for the listing, recognition, or classification in the name of another business name (usually a retailer or wholesaler), that is, the "AL" listing, recognition, or classification service. The difference between it and multiple listing, multiple recognition, or multiple classification services is that the applicant is not the listed entity.

6. System Certification Services:
As one of the members of the International Accreditation Forum, UL is widely involved in ISO9000 quality system certification, ISO14000 environmental protection certification, QS9000 automotive industry quality system certification, and AS9000 aviation industry quality system certification services. A total of 116 factories in China have obtained UL's system certification; among them, 21 are ISO9001 certified, 85 are ISO9002 certified, 1 is ISO14001 certified, and 9 are QS9000 certified.

7. Other Services of UL:
Such as certification services, inspection services, fact judgment services, research services, etc.

Process
Applying for the UL mark for a product includes the following steps:

1. The applicant submits relevant company and product information
Written application: You should request in writing that UL test your company's products.
Company information: Provide the following units' detailed and accurate names, addresses, contacts, postal codes, telephones, and faxes in both Chinese and English.
(a). Applying company: The company that submits the product testing application and is responsible for all engineering service fees.
(b). Listed company: The company whose name is listed in various product catalogs published by UL.
(c). Manufacturing factory: The manufacturer and producer of the product.
Product information: The product information should be provided in English.
(a). Product name: Provide the full name of the product.
(b). Product model: List in detail all product models, varieties, or classification numbers, etc. that need to be tested.
(c). Intended use of the product: For example, home, office, factory, coal mine, ship, etc.
(d). Parts list: List in detail the components and parts of the product and their models (classification numbers), ratings, and the names of the manufacturing companies. For insulating materials, please provide the name of the raw material, for example: GE Polycarbonate, Lexan Type 104. When the components have obtained UL certification or recognition, please prove the specific model of the component and indicate its UL file number.
(e). Electrical performance: For electronic and electrical products, provide electrical schematic diagrams (circuit diagrams) and electrical performance tables.
(f). Structure diagram: For most products, it is necessary to provide the product structure diagram or exploded view, ingredient list, etc.
(g). Product photos, usage instructions, safety items, or installation instructions, etc.

2. Make a decision based on the provided product information
When the product information is complete, UL engineers will make the following decisions based on the information: the UL standards on which the test is based, the engineering cost of the test, the test time, the number of samples, etc., and notify you in writing, and send the formal application form and follow-up service agreement to your company. The application form indicates the cost limit, which is the maximum engineering cost estimated by UL based on the test items. Without your company's written authorization, this cost limit cannot be exceeded.

3. The applying company remits the payment, sends back the application form, and samples
The applicant signs on the application form and the follow-up service agreement and sends the form back to UL. At the same time, remit the payment through the bank and send the samples by post or express delivery. Please provide an appropriate description of the samples submitted for testing (such as name, model). The application form and samples should be sent separately. For each application item, UL will assign a unique project number (Project No.). Indicate the project number and the name of the applying company when remitting the payment, sending the samples, and the application form for UL to check and receive.

4. Product testing
After receiving the signed application form, payment, and test samples from your company, UL will notify you of the completion time of the test plan. Product testing is generally carried out in UL laboratories in the United States. UL can also accept the test data of participating third parties after review. The test samples will be returned or destroyed according to your request.
If the product testing results meet the UL standard requirements, UL will issue a test pass report and follow-up service procedures (FollowUp Service Procedure). The test report will detail the test situation, the indicators achieved by the samples, the product structure, and the safety marks suitable for the product. The follow-up service procedures include a description of the product and instructions for UL regional inspectors. A copy of the test report will be sent to the applying company, and a copy of the follow-up service procedures will be sent to each manufacturing factory.

5. The applicant is authorized to use the UL mark
The UL regional inspector in China contacts the manufacturing factory for the initial production inspection (IPI). The inspector checks the situation of your products and their components on the production line and in the warehouse to confirm whether the product structure and components are consistent with the follow-up service procedures. If required in the procedures, the regional inspector will also conduct witnessed tests. When the inspection results meet the requirements, the applicant is authorized to use the UL mark.
After the IPI, the inspector will visit the factory periodically to check the product structure and conduct witnessed tests. The inspection frequency is determined by the product type and production volume. Most types of products are inspected at least four times a year. The inspector's inspection is to ensure that the product continues to meet the UL requirements. Before you plan to change the product structure or components, please notify UL in advance. For minor changes, there is no need to repeat any tests, and UL can quickly modify the follow-up service procedures to enable the inspector to accept such changes. When UL believes that the changes to the product affect its safety performance, the applying company needs to resubmit samples for necessary testing.
The cost of the follow-up service is not included in the testing cost.
If the product testing results do not meet the UL standard requirements, UL will notify the applicant and explain the existing problems. After the applicant improves the product design, the product can be resubmitted for testing. You should tell the UL engineer what improvements have been made to the product so that he can make a decision. The above are the steps for applying for UL certification.

Inspection Rules
Overview
The inspection by UL inspectors is basically a mechanical operation. Depending on different products, the inspection basis for inspectors includes Bulletins, Procedures, FUII (if available, included in the procedures), and UL standards (if required in FUII).
If the factory is producing UL products or has in-stock UL products when the inspector visits the factory, the inspector will sample the products in one of the following ways:

1. Select various components from the production line and a complete product from the warehouse.

2. Select various components from the warehouse and a complete product from the production line.

3. Select a complete product from the warehouse for disassembly.
The specific quantity of sampling is determined by the procedures, FUII (Follow-up Inspection Instructions), SAP (Standard Attachment Page), or direct orders from UL laboratories. Inspectors do not necessarily inspect all products during each inspection, but they will try to inspect all product categories or models within one year or at least two years.
Generally speaking, UL's requirements for the factory production system are not too high. It only requires annual calibration of instruments and equipment, proper preservation of the factory's own inspection records, and certain control measures for unqualified products.
During the inspection, the on-site representative (UL inspector) will focus mainly on the product itself. They will check the product structure, components, and assembly item by item according to the above inspection basis. For components related to product safety, the procedures generally specify that they should be UL-certified products and indicate the manufacturer and model; for injection-molded parts such as casings and shields, the procedures generally specify the requirements for their raw materials and dimensions. The on-site representative will check the above items and the UL marks specified in the procedures.

On-site Testing
In addition, if the procedures or FUII or standards require on-site testing of the product, the on-site representative will ask the factory inspector to conduct the corresponding tests, and the on-site representative will act as a witness. If the procedures also require sending samples to UL for follow-up testing, the factory should cooperate with the inspector to make the corresponding samples. After the inspector fills in the sample labels, provides the address, and seals the samples, the factory will send them to the corresponding UL laboratory.
If the products produced by the factory fully meet the requirements of the corresponding UL inspection standards and there are no other violations of the follow-up service agreement, the inspector will issue a follow-up inspection report (Inspection Report); the factory representative should sign on the report after confirming that the content is accurate; and the inspection is completed. If there are situations that do not conform to the inspection standards during the inspection process, the inspector will issue a variation notice (Variation Notice) and take corresponding measures according to the specific situation.

Removal of the UL Mark
For the unauthorized use of the UL mark on products, the inspector will require the removal of the UL mark; for products that do not meet the UL requirements, the inspector will require the factory to remove the UL mark or rework the products to make them meet the requirements. If the factory disagrees with the above handling opinions, it can temporarily retain the UL mark but must stop shipping the products. The inspector will notify the corresponding laboratory of the situation, and UL will make a reply to decide whether the UL mark can be retained. If there are only some minor problems that do not affect the safety of the product, the inspector will make a decision of temporary acceptance and report to the corresponding laboratory. If there are some obvious standard errors, such as typing errors or unit errors, it does not affect the qualification of the factory's products. However, as part of UL's document processing, the inspector will also issue a variation notice. Generally, unless it is the responsibility of UL, the inspector will require the factory to explain the non-conforming items to the corresponding laboratory, and UL will make a corresponding reply based on your explanation.

Final Decision-making Power
Of course, the inspector's judgment is only temporary, and the final decision-making power is, of course, in each UL laboratory. If the factory disagrees with the inspection methods, it can definitely report to the corresponding laboratory. At this time, the inspector is obliged to provide the corresponding contact person and contact method. After confirming that the content recorded in the variation notice is correct, the factory representative should sign on the notice.

UL Certification Factory Inspection
The UL regional inspector in China contacts the manufacturing factory for the initial production inspection (IPI). The inspector checks the situation of your products and their components on the production line and in the warehouse to confirm whether the product structure and components are consistent with the follow-up service procedures. If required in the procedures, the regional inspector will conduct witnessed tests. When the inspection results meet the requirements, the applicant is authorized to use the UL mark.
After the IPI, the inspector will visit the factory periodically to check the product structure and conduct witnessed tests. The inspection frequency is determined by the product type and production volume. Most types of products are inspected at least four times a year (the cost of the follow-up service is not included in the testing cost). The inspector's inspection is to ensure that the product continues to meet the UL requirements. Before you plan to change the product structure or components, please notify UL in advance. For minor changes, there is no need to repeat any tests, and UL can quickly modify the follow-up service procedures to enable the inspector to accept such changes. When UL believes that the changes to the product affect its safety performance, the applying company needs to resubmit samples for necessary testing.

Certification Review
Before the first batch of UL-certified products is shipped, the local provincial-level China Import and Export Commodity Inspection Bureau (CCIB) authorized by UL will send people to the factory for review. Follow-up inspections are also carried out every year.

Follow-up Inspection
Introduction
As an organic part of UL certification, in order to ensure that UL-listed and recognized products continue to meet UL standards and requirements, UL has developed a "follow-up inspection" system. "Follow-up inspection" means that UL sends on-site representatives located all over the world to the local factory production sites to conduct follow-up inspections of UL products. Its purpose is to ensure that the manufacturer's production process, inspection process, and products always meet UL requirements by checking the factory's production process, inspection process, and products against UL standards and follow-up inspection procedures.

Basis for Follow-up Inspection
After arriving at the factory, the on-site representative mainly conducts inspections according to the "Follow-up Inspection Procedures". The "Follow-up Inspection Procedures" are compiled by the UL Engineering Department after testing the submitted samples. This document includes a comprehensive description of the product, as well as photos, instruction manuals, etc. It also specifies various tests that the manufacturing factory should frequently conduct during production. Some of these tests require 100% inspection of the products, such as the withstand voltage test. Some inspections can be carried out by sampling. At the same time, it also specifies the test items that the on-site representative must randomly check during the factory inspection. The on-site representative judges whether the inspection results are qualified according to the detailed information and regulations of these tests.

Classification of Products for Follow-up Inspection
The review is divided into the initial review and the quarterly review. The cost of the initial review is relatively higher. UL's follow-up inspection is divided into Category R and Category L. Category L services are mainly used for products related to life safety, such as fire extinguishers, smoke detectors, fire doors, and some products with a relatively large production volume, such as electrical equipment, wires, and circuit breakers. For products belonging to Category L, the manufacturing factory must directly order labels from UL and affix them to the products. Category R services are mainly used for electrical equipment, such as electric fans, televisions, hair dryers, ovens, and other products that are usually produced on the corresponding production lines.

Technical Terms
"AL" LISTING (Multiple Listing or Recognition)
AGENT (Agent)
APPEALS PROCEDURE (Appeals Procedure)
APPENDIX (Appendix)
APPLICANT (Applicant)
AUTHORIZATION PAGE (Authorization Page)
CATEGORY CONTROL NUMBER (Category Control Number)
COMPONENT (Component)
CONDITION OF ACCEPTABILITY (Condition of Acceptability)
CONTROL NUMBER (Control Number)
FACTORY IDENTIFICATION (Factory Identification)
FACTORY INSPECTION (Factory Inspection)
"AL" LISTING, CLASSIFICATION OR RECOGNITION (Multiple Listing or Recognition)
A listing or recognition service established in the name of another party different from the applicant (the listed party), upon the application and authorization of the applicant.
AGENT (Agent)
An individual or enterprise entrusted by the applicant to conduct activities with UL in the name of the applicant.
APPEALS PROCEDURE (Appeals Procedure)
If the customer has different opinions on the results of the engineering test or follow-up inspection, they can discuss with the relevant engineer or on-site representative without worrying about endangering future conclusions. If a satisfactory reply cannot be obtained at this level, the customer can file an appeal to a higher level, up to the president.
APPENDIX (Appendix)
A part of the procedures, which includes the responsibilities of the factory and the on-site representative, as well as the requirements for relevant tests. It may also describe the tests conducted on the samples sent to UL.
APPLICANT (Applicant)
An enterprise or individual who applies to UL for testing its components, products, or systems. Legally, this party is responsible for the fees of the testing and follow-up services and has the right to all information related to the test results. See also Agent.
AUTHORIZATION PAGE (Authorization Page)
The page at the front of the factory inspection procedures for follow-up services, which authorizes the corresponding follow-up inspection service (Category L or Category R) and the permitted certification marks.
CATEGORY CONTROL NUMBER (CCN) (Category Control Number)
The character representation of different product categories in UL's listing, recognition, and classification services. For example, AVLV2 represents electronic wires; QOWZ represents portable lighting fixtures. Generally, XXXX represents listed products, XXXX2 represents recognized products, XXXX7 represents listed products that meet Canadian standards, and XXXX8 represents recognized products that meet Canadian standards.
COMPONENT (Component)
A part of the product. In addition to participating in the testing of the entire product as part of the complete product, its performance and/or structure also need to be tested separately. Components can be listed, recognized, or unlisted parts.
CONDITION OF ACCEPTABILITY (Condition of Acceptability)
These items are listed in the reports of recognized or unlisted components, but they are not used as the basis for the on-site representative's inspection. These items, based on the test results, indicate the restrictions and conditions when the component is used in the complete product. For example, in the report of a certain switch, it may be specified in the "Condition of Acceptability" that the product is only suitable for currents below 1A or temperatures below 125°C.
CONTROL NUMBER (Control Number)
One of the four possible components of the UL recognition mark, designated by UL. Depending on different product categories and different types of follow-up services, the control number may be changed periodically.
FACTORY IDENTIFICATION (Factory Identification)
An identification mark adopted by the manufacturer producing the same product in different factories to distinguish which factory a certain product is produced in.
FACTORY INSPECTION (Factory Inspection)
Industries of Concern for UL Certification
Audio-visual Equipment
Automobiles
Components
Household Appliances
Industrial Control Equipment
Information Technology Equipment
Lighting Fixtures
Medical Devices
Plastics
Information Equipment
Wires and Cables
UL Convincing with Data
UL94 Certification - Test Items
The evaluation of plastic materials in UL94 certification is not only about the flame-retardant performance but also includes the analysis and testing of the thermal and electrical properties of plastics. In addition, the thermal aging performance of plastics under long-term exposure to high temperatures (thermal aging in an air oven), water, ultraviolet rays, cold, etc. are all used as the final evaluation of the materials.
The performance evaluation of materials in UL94 certification includes:
UL Certification for 94 Flammability
UL Certification for 746A Electrical and Mechanical Properties
UL Certification for 746B Thermal Aging Procedure
UL Certification for 746C Review File
Outdoor Adaptability of Plastics
Component QMQS2
Color QMLJ2
Materials used in special environments are for maintaining the required performance in product applications where the materials are used for specific final investigations after being exposed to certain key operating and/or environmental conditions. This will include exposure to different types of ultraviolet (UV) radiation.